1. Field of the Invention
The present invention relates to a vane pump which is incorporated in a transmission case of a continuously variable transmission.
2. Description of Related Art
A continuously variable transmission (hereinafter referred to as CVT) has a transmission case equipped with a gear pump therein, and an operating oil supplied from the gear pump operates each part of the CVT. Since a pump efficiency of the gear pump, however, is not so good, use of a vane pump having better pump efficiency as compared to the gear pump has started to be reviewed. The vane pump is incorporated in the transmission case for use in the same way with a general gear pump, and an inside of the transmission case is filled with the operating oil. Accordingly, the vane pump is in a state to be submerged in the operating oil by more than the half thereof.
FIG. 2 shows a vane pump used under such a condition (refer to Japanese Patent Publication JP8-291793A).
The CVT includes a pump case 20 constructed of a body 1 and a cover 2. A cam ring 4 is incorporated in a body bore 3 formed in the body 1. A rotor 5 is disposed inside the cam ring 4. A plurality of vane grooves 6 are radially formed in the rotor 5, and a vane 7 is incorporated in each vane groove 6 in such a way to freely retract into or move out of the vane groove 6. A pump discharge pressure is introduced to a backpressure groove 6a as the bottom of the vane groove 6.
A drive shaft 8 is inserted in the pump case 20. The drive shaft 8 is rotatably supported by a bearing 9a in the body 1, as well as penetrates through the rotor 5 and is rotatably supported at the penetrating end by a bearing 10 disposed in the cover 2. The drive shaft 8 is arranged to be engaged to the rotor 5 via serration for rotation integral therewith.
Further, as an example, a base end of a drive shaft 8, i.e. an opposing side thereof to the side of the cover 2 extends into the transmission case (not shown). A driving mechanism is disposed in the transmission case and the drive shaft 8 is associated with the drive mechanism. The vane pump is, as described above, buried in the operating oil and therefore, a seal member 11 is not necessarily required, but may be disposed for sealing the circumference of the drive shaft 8.
Under the above structure, when the driving mechanism is rotated in the transmission case to rotate the drive shaft 8, the vanes 7 retract into or move out of the vane grooves 6, while rotating along an inner peripheral surface of the cam ring 4 together with the rotor 5. During this rotating process of the vanes 7, the chambers defined between the plurality of the vanes expand or contract to suck in or discharge the operating oil, i.e. provide a pumping action.
When the pumping action is provided as described above, the operating oil is drawn from a suction port 12 disposed in the body 1. The suction port 12 is arranged to have a suction opening positioned lower than the oil level in the transmission case and also oriented directly below. As a result, the operating oil in the transmission case is drawn directly from the suction port 12.
The operating oil drawn from the suction port 12 is drawn via a suction flow passage 13 formed in the side of the cover 2 into chambers defined by the vanes 7 during an expansion stroke and is then discharged from the same chambers during a contraction stroke. The high-pressure operating oil discharged from the chambers defined by the vanes 7 is introduced from a high-pressure chamber 14 via a passage (not shown) into a flow control valve 15.
The flow control valve 15 to which the high-pressure operating oil is introduced supplies a predetermined flow quantity thereof to a piston activating a pulley of the CVT (not shown) or a CVT drive mechanism such as a forward/backward changing apparatus and returns an excessive flow quantity of the operating oil exceeding the predetermined flow quantity back to the suction flow passage 13. The necessary flow quantity of the operating oil other than the excessive flow quantity is supplementary from the suction port 12.
In addition, the high-pressure operating oil discharged into the high-pressure chamber 14 is also introduced to the backpressure grooves 6a of the vane grooves 6 and with action of the high-pressure oil introduced to the backpressure grooves 6a, the vanes 7 are pushed out of the vane grooves 6 to contact the vanes 7 with the inner peripheral surface of the cam ring 4.
When the vane pump is driven to generate a high pressure in a discharge path side, the operating oil is leaked from a clearance between each member. The high-pressure operating oil discharge to the high-pressure chamber 14 is, for example, introduced into the flow control valve 15 via a passage (not shown), and during the communicating process, a leaked oil flows into a clearance between a shaft bore 9 of the body 1 and the drive shaft 8. The leaked oil flown between the shaft bore 9 and the drive shaft 8 is returned back to the side of the suction flow passage 13 via a drain passage 16. Accordingly, the leaked oil is arranged to be again drawn in the pump via the drain passage 16.